After months of speculation, Kate Middleton is finally, officially, pregnant. And she can’t even enjoy it.

Middleton is tethered to an IV in King Edward VII Hospital in London, where she’s spending her second day being treated for symptoms that match up with hyperemesis gravidarum. In other words, she’s throwing up. A lot.

Pregnancy-associated nausea is common — it’s often referred to as morning sickness, although it can strike at any time of the day — but the extreme nausea and vomiting associated with hyperemesis affects less than 2% of pregnant women.

Why it happens is a mystery. It’s thought to be related to hormonal spikes in estrogen, progesterone and hCG (human chorionic gonadotropin, which is detected by pregnancy tests). Sluggish digestion during pregnancy may also be a factor.

Many women suffering from hyperemesis respond to oral anti-nausea medication, but in Middleton’s case, Prince William reportedly rushed her in his Range Rover to the hospital. It’s not the hyperemesis itself that’s so worrisome; it’s the risk of losing too much fluid. “I am sure her doctors are being cautious, but some women need hospitalization to prevent dehydration,” Dr. Samantha Pfeifer, an associate professor of obstetrics and gynecology at the University of Pennsylvania, said in an email explaining the condition.

That’s the purpose of Middleton’s IV; she may also be receiving intravenous anti-nausea drugs. In the most severe cases in which food can’t be kept down, TPN, or total parenteral nutrition, may be administered via IV.

“Kate Middleton is very thin and I bet that she has low blood pressure so if she got dehydrated she could pass out easily,” Dr. Ruth Ann Crystal, an obstetrician in Palo Alto, Calif. who is known on Twitter as @CatchTheBaby, said via email.

As for rampant rumors about Middleton carrying twins, the jury is out. Twins can increase the risk of extreme nausea — as can carrying a girl — but that’s not necessarily the case. As any mother knows, morning sickness can be worse during some pregnancies, regardless of whether the child is a boy or girl. Unless Middleton and her prince announce the gender a few weeks down the road, we’ll all have to wait until late summer, when it seems the heir — or heirs — to the throne would be due.

Research out of Canada looked specifically at the link between prenatal vitamins and it has shown it is the iron which doctors prescribe to pregnant women that causes the mornng sickness. "The effectiveness of discontinuing iron-containing prenatal multivitamins on reducing the severity of nausea and vomitingof pregnancy." "Avoiding iron-containing multivitamins is effective in majority". http://www.ncbi.nlm.nih.gov/pubmed/19280488